Molten salt catalytic compositions and methods for the cracking of carbon-containing feedstocks

ABSTRACT

A catalyst composition includes a metal catalyst dispersed in a molten eutectic mixture of alkali metal or alkaline earth metal carbonates or hydroxides. A process for the catalytic cracking of hydrocarbons includes contacting in a reactor system a carbon-containing feedstock with at least one catalyst in the presence of oxygen to generate olefinic and/or aromatic compounds; and collecting the olefinic and/or aromatic compounds; wherein: the at least one catalyst includes a metal catalyst dispersed in a molten eutectic mixture of alkali metal or alkaline earth metal carbonates or hydroxides. A process for preparing the catalyst includes mixing metal catalyst precursors selected from transition metal compounds and rare-earth metal compounds and a eutectic mixture of alkali metal or alkaline earth metal carbonates or hydroxides and heating it. A use of the catalyst in the catalytic cracking process of hydrocarbons.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/334,474 filed on May 28, 2021, which claims the benefit of andpriority to U.S. Provisional Application No. 63/032,210, filed May 29,2020, the contents of which are incorporated herein by reference intheir entirety.

FIELD

The present technology is generally related to catalysis for thecracking of carbon-containing feedstocks. More specifically, it isrelated to molten salt compositions for catalyst compositions andmethods of cracking in the presence of an oxidant to form olefinic andaromatic monomers from a carbon-containing feedstock.

SUMMARY

Oxycracking is an attractive route for the direct conversion ofcarbon-containing feedstocks (e.g., waste plastics, bio-based complexcompositions, light alkanes, and municipal solid waste) into value-addedbasic chemical building blocks (e.g., olefins, oxo-compounds, andaromatics). The direct conversion of carbon-containing feedstocksreduces carbon dioxide emissions usually associated with the productionof value-added basic chemical building blocks. One way to performoxycracking relies on the use of a molten salt catalyst, and the presentinventors have found that the molten salt catalyst can improve theprocess efficiency.

In one aspect, a heterogeneous catalyst composition is provided thatincludes a metal catalyst dispersed in a molten salt matrix comprising aeutectic mixture of alkali metal or alkaline earth metal carbonates orhydroxides. In some embodiments, the metal catalyst includes atransition metal compound, a rare-earth metal compound, or a mixture ofa transition metal compound and a rare-earth metal compound. In someembodiments, the eutectic mixture is a mixture of alkali metal oralkaline earth metal carbonates or hydroxides having a melting point ofless than about 750° C.

In another aspect, a process is provided for catalytic cracking ofhydrocarbons, where the process includes contacting in a reactor systema carbon-containing feedstock with at least one heterogeneous catalystin the presence of an oxidant to generate olefinic and/or aromaticcompounds; and collecting the olefinic and/or aromatic compounds; andwherein the at least one heterogeneous catalyst comprises a metalcompound dispersed in a molten salt matrix of a eutectic mixture ofalkali metal or alkaline earth metal carbonates or hydroxides. Theprocess may be an autothermal process.

In another aspect, a process is provided for preparing a heterogeneouscatalyst, where the process includes combining alkali metal or alkalineearth metal carbonates or hydroxides to form salt matrix comprising aeutectic salt mixture; adding to the salt matrix, at least one metalcatalyst precursor to form a catalyst precursor mixture; and heating thecatalyst precursor mixture to a temperature of about 250° C. to about750° C. to form the heterogeneous catalyst comprising a metal catalystdispersed in a molten salt matrix; wherein the metal catalyst precursorincludes at least one transition metal compound, rare-earth metalcompounds, or a combination of any two or more thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a ternary phase diagram for lithium, sodium, and potassiumcarbonates as reproduced from Chen et al. J. Sol. Energy Eng. 136(3):031017 (August 2014).

FIG. 2 is a flow chart for one embodiment of the method of crackingusing a heterogeneous catalyst composition described herein.

FIG. 3 is a flow chart for another embodiment of the method of crackingusing a heterogeneous catalyst composition as described herein andincluding a catalyst regeneration loop.

FIG. 4 is a general schematic representation of a reactor system for theprocessing of polymer waste.

FIG. 5 is a schematic diagram of a batch reactor set-up, according tothe examples.

FIG. 6 is a differential scanning calorimetry (DSC) trace for theformation of a eutectic melt from a mixture of Li₂CO₃, Na₂CO₃, and K₂CO₃powders, according to the examples.

FIG. 7 is a representative GC-MS (gas chromatography-mass spectrometry)trace showing the peak assignments based on the mass-spectra signaturesmatch with the NIST-MS database for an experiment of direct oxycrackingof a vegetable (olive) oil over the Li₂CO₃—Na₂CO₃—K₂CO₃ (43.5-31.5-25mol %) eutectic mixture in a mini-batch reactor. The experimentalconditions are described in the upper right corner insert box.

FIG. 8 includes GC-MS traces for the products collected directoxycracking of olive oil without a catalyst, and with Cat. E and Cat. Fin a mini-batch reactor, according to the examples.

FIG. 9 includes GC-MS traces for the products collected from directoxycracking of n-hexane in the presence of Li₂CO₃—Na₂CO₃—K₂CO₃(43.5-31.5-25 mol %) eutectic mixture, and of Cat. A′ in a mini-batchreactor, according to the examples.

FIG. 10 includes GC-MS traces for the products collected from 2-stepoxycracking of HDPE in the presence of Cat. A, Cat. B, Cat. C, and Cat.D, in a mini-batch reactor according to the examples.

FIG. 11 includes GC-MS traces for the products collected from 2-stepoxycracking of various feedstocks in the presence of Cat. A in amini-batch reactor, according to the examples.

FIG. 12 includes GC-MS traces of liquid products collected from a 2-stepoxycracking process that was performed in a stirred tank reactor in thepresence of Cat. A′, according to examples.

DETAILED DESCRIPTION

Various embodiments are described hereinafter. It should be noted thatthe specific embodiments are not intended as an exhaustive descriptionor as a limitation to the broader aspects discussed herein. One aspectdescribed in conjunction with a particular embodiment is not necessarilylimited to that embodiment and may be practiced with any otherembodiment(s).

As used herein, “about” will be understood by persons of ordinary skillin the art and will vary to some extent depending upon the context inwhich it is used. If there are uses of the term which are not clear topersons of ordinary skill in the art, given the context in which it isused, “about” will mean up to plus or minus 10% of the particular term.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the elements (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein may beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the embodiments and does not pose alimitation on the scope of the claims unless otherwise stated. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential.

As used herein, the term “dispersion” refers to a system in whichparticles of one material are distributed in a continuous phase ofanother material. The two phases may be in the same or different statesof matter, i.e., a solid metal catalyst dispersed in a molten alkalimetal or alkaline earth metal carbonate eutectic mixture melt.Dispersions are classified in several ways, including how large thedispersed particles are in relation to the particles of the continuousphase, and whether or not a spontaneous precipitation (sedimentation)occurs. In general, dispersions of particles sufficiently large forsedimentation are called suspensions, while those of smaller particlesare called colloids, and even smaller are called solutions. Inapplication to this invention the metal catalyst dispersed in the moltenmatrix can be a suspension, or it can be a colloid, or it can be asolution. The boundary between the cases of a bulk metal catalyst and adispersed metal catalyst is in the average particle size of 10 mm(cross-section distance from one side to the other side for a particle).It can be said that a bulk metal catalyst has an average particle sizeof >10 mm, while a dispersed metal catalyst has an average particle sizeof ≤10 mm. Another commonly found descriptor for the boundary case isthe geometric surface area of the dispersed material. In this case abulk metal catalyst has a geometric surface area of <0.01 meter squareper gram of metal catalyst material, while a dispersed metal catalysthas a geometric surface area of ≥0.01 meter square per gram of the metalcatalyst material.

As used herein, the term “cracking” refers to a chemical process wherebya feedstock, i.e. complex organic molecules such as long-chainhydrocarbons, carbohydrates, or others are broken down into simplermolecules such as light hydrocarbons, oxygenates, or carbon oxides bythe breaking of chemical bonds in the feedstock.

As used herein, the term “thermocracking” refers to a cracking process,whereby the conversion of feedstock to products is achieved by thermalenergy transfer, i.e. heating, and, hence, it requires operating atelevated temperatures to proceed.

As used herein, the term “oxycracking” refers to a cracking process thatutilizes a combination of thermocracking and oxidation processes,generally applied to the processing of heavy carbon-containingfeedstocks, resulting in the formation of lighter hydrocarbons products,plus some amounts of organic oxygenates, CO, CO₂, and H₂O as theco-products.

As used herein, the term “reactor system” refers to where the catalyticcracking reaction(s) take place. The process for catalytic cracking ofhydrocarbons may occur in a single reactor or in at least two reactorsin series.

As used herein, the term “at least one heterogeneous catalyst” refers tothe possibility of introducing more than one heterogeneous catalyst inthe reactor system of the process for catalytic cracking ofhydrocarbons. Hence, one or more than one heterogeneous catalyst may bein contacted with the carbon-containing feedstock in a single reactor orseparated in at least two reactors in series. At least one heterogeneouscatalyst may be equal or different from each other.

As used herein, the term “carbon-containing feedstock” is not onlypurely hydrocarbon materials as would typically be associated with theterm, but as long as there is a carbon-containing segment within aplastic (i.e. polymer) or biomass or biowaste that is amenable tocracking with the catalyst compositions provided herein, it meets thedefinition. For example, the carbon-containing feedstock may containoxygen in the material, as well as other heteroatoms (N, P, S, Cl, etc.)and other materials such as fillers (including silica, zinc oxide,titanium oxide, calcium carbonate, etc.), colorants, plasticizers, andthe like typically associated with polymers.

As used herein, the term “eutectic” or “eutectic mixture” refers to ahomogeneous mixture of substances that melts or solidifies at a singletemperature that is lower than the melting point of any of theconstituents. It does not necessarily refer to the lowest melting pointthat is achievable with any particular mixture of substances, this isthe eutectic point for those substances, and it may be part of theeutectic mixture. As long as a mixture of substances melts at atemperature lower than the melting point of any of its constituting puresubstances, and forms a single continuous phase, it is a “eutectic” or“eutectic mixture” for the purposes of this disclosure. As used herein,the phrase “a eutectic mixture of alkali metal or alkaline earth metalcarbonates or hydroxides” may be alternatively recited as “a eutecticmixture of alkali metal carbonates, alkali metal hydroxides, alkalineearth metal carbonates, alkaline earth hydroxides, or a mixture of anytwo or more thereof.”

It has now been found that the cracking of carbon-containing feedstocksmay be conducted in the presence of oxygen as an oxidant, which can be afree oxygen gas (O₂) or oxygen bound to catalyst, and a molten saltcatalyst to form a product stream containing olefinic and/or aromaticcompounds. The methods may be applied to carbon-containing feedstocksand includes recycling of olefinic polymers and biopolymers alike. Themethods may be applied to pure hydrocarbon feedstock streams as well asmixed streams, particularly where the hydrocarbon stream is from a mixedwaste recycling operation. The described methods and catalysts have thepotential to deliver improved performance over industry accepted methodssuch as thermal pyrolysis, thermal-steam cracking, fluid catalyticcracking, and supercritical fluid cracking. The cracking of thehydrocarbons on the molten salt catalyst is a heterogeneous process,hence reference to a “heterogeneous catalyst” or “heterogeneouscatalytic process.” Where free oxygen gas (O₂) is used in the process,the process is called “direct oxycracking.” Where the catalyst-boundoxygen is used in the process, the process is called “2-stepoxycracking.” In the 2-step oxy-cracking, the Step 1 is the reaction ofa hydrocarbon feed with the catalyst-bound oxygen (i.e., metal oxidelattice oxygen, or surface adsorbed form of oxygen), which results inthe loss of bound oxygen to the reaction products and the formation ofan oxygen-deficient (e.g., spent) form of catalyst. The Step 2 is thereaction of catalyst regeneration where the oxygen-deficient form of thecatalyst reacts with free oxygen gas to restore the catalyst to itsnative oxidized form. The catalyst in such a 2-step process alsoperforms the function of an oxygen carrier.

The methods described herein take advantage of autothermal crackingprocesses where the thermal demands for the process are met by all, orat least part of, the internally generated heat by taking advantage ofthe exothermic process. Other accepted processes in the industry relyentirely on externally generated heat to achieve the desired conversion,and, because of this, are more energy and capital-intensive processes.

The present methods are also a fast-cracking process, due to thepresence of both oxygen and molten catalyst, allowing for lowerprocessing temperatures (i.e., less than 750° C.). Alternative crackingprocesses, such as thermal- and thermal-steam cracking, require a muchhigher temperature, typically greater than about 850° C., in order toachieve similar productivity output per reactor unit of volume. Further,the present methods require only a moderate pressure inside the reactor,i.e., less than about 20 atmospheres (“atm”). Alternative crackingprocesses, such as supercritical fluid cracking and high-pressurecatalytic cracking, utilize much higher processing pressures, and,because of this, are more energy and capital-intensive processes.

The methods described herein also tolerate the presence of acidimpurities, such as those containing chloride, bromide, sulfide,sulfate, and phosphate groups in the feed. The method also tolerates thepresence of plastic filler components, such as silica, titania, zincoxide, calcium carbonate, and others. The removal of such acidimpurities and plastic filler components is believed to occur throughthe absorption of such materials into the eutectic mixture, which isthen purified, and the impurities removed. Thus, the method is feedstockflexible and can be used to process mixed plastic waste. The methods mayalso be operated as a continuous, semi-continuous, or batch processes.Thus, the method offers a high degree of flexibility for its end-userapplication design and operation.

Without being bound by theory, the reaction is believed to proceedaccording to the following eight equations and summarized as equation(9). In equation (1) a catalytic oxycracking is described for apolyolefin feed reacting with oxygen in the presence of a catalyst at atemperature of less than about 750° C., or less than about 650° C. Thecatalyst is a molten salt mixture of alkali metal or alkaline earthmetal carbonates or hydroxides with a metal catalyst. The product of thereaction is an aldehyde.

When a sufficient amount of oxygen is present, the aldehyde product fromequation (1) can undergo further oxidation forming a carboxylic acidaccording to equation (2).

Within the same reactor, several other reactions as described byequations (3-4) are also believed to be taking place. Equation (3) is adeoxygenation reaction via the catalytic conversion of the aldehyde overthe catalyst to the olefin, with carbon monoxide and hydrogen forming asco-products.

Equation (4) is a deoxygenation reaction via the catalytic conversion ofthe carboxylic acid over the catalyst to the olefin, with carbon dioxideand hydrogen as co-products.

The catalyst, which is a molten salt mixture of alkali metal or alkalineearth metal carbonates or hydroxides with metal compound, can be abifunctional catalyst, because it accelerates both oxycracking anddeoxygenation reactions simultaneously.

Within the same reactor, several secondary reactions as described byequations (5-8) are also believed to be taking place. These reactionscan proceed on their own or be accelerated by the presence of catalyst.Equation (5) is a hydrogenation reaction via the conversion of an olefinand hydrogen to an alkane.

Equation (6) is a reverse water-gas shift reaction via the conversion ofcarbon dioxide and hydrogen to carbon monoxide and water.

Equation (7) is a disproportionation, which is also known as theBoudouard reaction, reaction via the conversion of two equivalents ofcarbon monoxide to one equivalent of carbon dioxide and one equivalentof free carbon (i.e., coke).

Finally, when certain excess of oxygen present, Equation (8) is anoxidation reaction via the conversion of one equivalent of free carbonwith two equivalents of oxygen to one equivalent of carbon dioxide.

Catalyst can be selected such that the overall reaction is shown byreference to Equation (9):

As provided in Equation (9), the overall reaction is exothermic andprovides heat to sustain itself. The standard enthalpy of reaction forequation (9) is estimated to be approximately −97 kcal/mol. It isnoteworthy that the thermal degradation of polyethylene (—(CH₂CH₂)_(n)—)in the absence of the catalyst system and oxygen is an endothermicreaction having an enthalpy of reaction estimated as +25.4 kcal/mol.

In a first aspect, a heterogeneous catalyst composition is provided thatincludes a metal catalyst dispersed in a molten salt matrix of aeutectic mixture of alkali metal or alkaline earth metal carbonates orhydroxides. The metal catalyst may include at least one metal compoundselected from the group of transition metal compounds, rare earth metalcompounds, or a combination of any two or more thereof. The eutecticmixture is the basis for the molten salt matrix, and it melts at a lowertemperature than its constituent materials, and it melts at atemperature at which the catalytic reactions may be conducted to formdesirable materials from a feedstock.

The eutectic mixture of alkali metal carbonates and hydroxides may be amixture of Li, Na, and K carbonates or hydroxides. In some embodiments,the eutectic mixture is one of Li₂CO₃, Na₂CO₃, and K₂CO₃. FIG. 1 is aphase diagram reproduced from Chunlin Chen, Ty Tran, Rene Olivares,Steven Wright, Shouyi Sun; J. Sol. Energy Eng. August 2014, 136(3):031017, illustrating the melting points for a wide variety of Li, Na,and K carbonates mixtures. In some embodiments, the eutectic mixture ofalkali metal carbonates or hydroxides has a melting point of less thanabout 750° C., or less than about 650° C. This includes melting pointsfrom about 250° C. to about 650° C., from about 350° C. to about 550°C., or about 400° C. Other illustrative eutectic mixture of alkali metalcarbonates includes those in Table 1, reproduced from Mutch et al. J.Mater. Chem. A 7, 12951-12973 (2019).

TABLE 1 Melting points of the individual alkali- carbonate saltcompounds and their eutectic mixtures. Melting Salt System Point (° C.)Li₂CO₃ 723 Na₂CO₃ 854 K₂CO₃ 891 Li₂CO₃—Na₂CO₃ (52-48 mol %) 501Li₂CO₃—K₂CO₃ (62-38 mol %) 498 Na₂CO₃—K₂CO₃ (56-44 mol %) 710Li₂CO₃—Na₂CO₃—K₂CO₃ (43.5-31.5-25 mol %) 397 Na₂CO₃—BaCO₃ (52.2-47.3 mol%) 686

Where the eutectic mixture includes a hydroxide of Li, Na, and/or K atthe beginning of a process employing such a mixture, it should be notedthat the processes described herein generate CO₂ as a byproduct.Accordingly, with CO₂ generation at the operating temperatures of themolten salt, any alkali or alkaline earth metal hydroxides are readilyconverted to the corresponding carbonates.

In one embodiment, the transition metal compound that is included in themetal catalyst may include a transition metal having catalyticproperties, and its incorporation into the catalyst composition may beas a transition metal carbonate, a transition metal salt of an organicacid, or a transition metal oxide. The transition metal may be basedupon a Group 4-12 metal. Illustrative transition metals may include, butare not limited to, one or more of V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo,and W. In some embodiments, the transition metal is one or more of Mn,Fe, Ni, Cu, Co, and W. In some embodiments, the transition metalcompound may include a carbonate of one or more of Mn, Fe, Co, Ni, andCu. In other embodiments, the transition metal compound may include asalt of an organic acid of one or more of Cr, Mn, Fe, Co, Ni, Cu, andZn, where the organic acid is derived from formic acid, acetic acid,propionic acid, butyric acid, hexanoic acid, oxalic acid, tartaric acid,lactic acid, oleic acid. And, in further embodiments, the transitionmetal compound may include an oxide of one or more of V, Cr, Mn, Fe, Co,Ni, Cu, Zn, Mo, and W.

In one embodiment, the rare earth metal compound that is included in thecatalyst may be introduced as a rare earth metal carbonate, a rare earthmetal salt of an organic acid, or a rare earth metal oxide. Illustrativerare earth metals include, but are not limited to, one or more of La,Ce, Pr, and Nd. In some embodiments, the rare earth metal compound is arare earth metal carbonate that is a carbonate of one or more of La, Ce,Pr, and Nd. In some embodiments, the rare earth metal carbonate is acarbonate of Ce. In other embodiments, the rare earth metal compound mayinclude a salt of an organic acid of one or more of La, Ce, Pr, and Nd,where the organic acid is derived from formic acid, acetic acid,propionic acid, butyric acid, hexanoic acid, lactic acid, oleic acid.And, in further embodiments, the rare earth metal compound may includean oxide of one or more of La, Ce, Pr, and Nd. It is noted that underthe conditions of the formation of the eutectic mixture and reactionsdescribed herein, the transition metal compounds or rare earth metalcompounds, if other than a carbonate or oxide, is likely converted tothe carbonate or oxide during the course of the reaction(s). Thus, thetransition metal compounds, or rare earth metal compounds added to themixture of salts may be a precursor to the carbonate or oxide catalyst.

In any of the embodiments herein, a mixture of a transition metalcompound and a rare earth metal compound may include a mixture of Cu,and Ce, and the eutectic mixture of alkali metal carbonates orhydroxides includes a mixture of Li, Na, and K. As an illustrativeexample, in some embodiments, the transition metal compound includes amixture of CuCO₃, and Ce(CO₃)₂. In some such embodiments, the eutecticmixture of alkali metal carbonates or hydroxides may include a mixtureof Li₂CO₃, Na₂CO₃, and K₂CO₃. In other embodiments, the transition metalcompound includes a mixture of Cu₂(OH)₂CO₃, and Ce₂(CO₃)₃·xH₂O, and themolten salt matrix Li₂CO₃, Na₂CO₃, and K₂CO₃. Where such compounds arepresent, the mixture of a transition metal compound and a rare-earthcompound may include the Cu, and Ce in a mol % ratio of about0.10-0.20:1.00, respectively. The molten salt may include the Li, Na,and K in a mol % ratio of about 43:32:25.

In any of the embodiments herein, a mixture of a transition metalcompound may include a mixture of La and Fe, and the eutectic mixture ofalkali metal carbonates or hydroxides includes a mixture of Li, Na, andK. As an illustrative example, in some embodiments, the transition metalcompound includes a mixture of La(OH)₃, Ba(CO₃)₂, and FeCO₃. In somesuch embodiments, the eutectic mixture of alkali metal carbonates orhydroxides may include a mixture of Li₂CO₃, Na₂CO₃, and K₂CO₃. Wheresuch compounds are present, the mixture of a transition metal compoundand rare earth metal compound may include the La, Ba and Fe in a mol %ratio of about 0.03-0.04:0.03-0.04:1.00, respectively. The molten saltmay include the Li, Na, and K in a mol % ratio of about 43:32:25.

Before describing the process in more detail, as well as the reactor, itis noted that, overall, the process described herein is an oxycrackingprocess. In other words, it is an oxygen-assisted thermocracking ofhydrocarbons. Like conventional thermocracking, the method is capable ofproducing light olefins and aromatic hydrocarbons as its primary output,but at relatively lower process temperatures, which can result in aneconomic benefit to the practitioner. The use of oxidant as a processco-feed is needed in making the cracking reaction inside the volumenet-exothermic, i.e., self-heating. This enables the reaction to producecomparable product yields at lower temperatures due to higher thermalefficiency. Albeit, this benefit comes as a cost, as a fraction of thehydrocarbon feed is now consumed as a form of internal fuel to generatethe necessary heat. While for processing some type of feeds, this feedloss is economically detrimental, for processing of waste plastics,bio-wastes, and other low-quality feeds, the economic benefit can besignificant. This economic benefit can further be improved by applying acatalyst to the oxycracking process that has been specifically designedto maximize the yield of light olefin and aromatics products; minimizethe yield of the reaction byproducts such as alkanes, organic oxygenatesand heavies; and to solve technical hurdles that are specific to theprocessing of waste plastics streams, including the presence ofheteroatom functionalities, fillers, modifiers, etc. in the processfeed.

In the oxycracking process, a carbon-containing feedstock is injectedinto a reactor system where it comes into contact with a form of oxygen,which can be either a free oxygen gas (O₂), or a catalyst-bound form ofoxygen, or both, and a catalyst. The upper temperature limit within thereactor is defined by the need to preserve a substantial fraction of thecarbon-carbon bonds of the feed from the thermo-pyrolytic decomposition.For example, for a polyethylene feed, the limit is defined by a ceilingtemperature of about 610° C. For those familiar with the art, acommercial process designed for thermocracking of polyethylene canoperate at a temperature exceeding the ceiling temperature by 50-150° C.in order to achieve economically practical feed-to-monomers conversionrates. In the case of other feeds, the upper temperature limit is afunction of the ceiling temperatures of the corresponding monomers, asgiven in the values in Table 2, reproduced from Stevens, M.P. PolymerChemistry an Introduction (3rd ed.). New York: Oxford University Press.pp. 193-194 (1999), plus the additional 50-150° C. to achieve practicalrates:

TABLE 2 Ceiling temperatures of common hydrocarbon monomers. MonomerCeiling Temperature (° C.) Structure ethylene 610 CH₂═CH₂ 1,3-butadiene585 CH₂═CHCH═CH₂ isoprene 466 CH₂═C(Me)CH═CH₂ styrene 395 PhCH═CH₂methyl methacrylate 198 CH₂═C(Me)CO₂Me isobutylene 175 CH₂═CMe₂α-methylstyrene  66 PhC(Me)═CH₂

The lower temperature limit is defined by the need to maintain thecatalyst in the liquid state. As an illustration, this is about 397° C.for the Li₂CO₃—Na₂CO₃—K₂CO₃ (43.5-31.5-25 mol %) eutectic mixture, about283° C. for a NaOH—Na₂CO₃ (90-10 mol %) eutectic, about 360° C. for aKOH—K₂CO₃ (90-10 mol %) eutectic, about 170° C. for a NaOH—KOH (57-43mol %) eutectic, and about 226° C. for a LiOH—KOH (30-70 mol %)eutectic. Because the underlying chemistry, in essence, is a partialoxidation, the reaction rate benefits from an increased pressure ofoxygen gas in the feed. In practical terms, the oxycracking process canbe performed from a sub-atmospheric to a moderately elevated pressure(20 atm) range of the oxygen gas (i.e., air) feed in order to minimizethe risk of thermal run-aways for the safety reasons.

In another aspect, a process for the catalytic cracking of hydrocarbonsis provided that incorporates any of the described catalystcompositions. The process may include contacting in a reactor acarbon-containing feedstock with at least one catalyst composition, inthe presence of oxygen, to generate olefinic and/or aromatic compounds.The process further includes collecting the olefinic and/or aromaticcompounds. As noted above, at least one catalyst is any of those asdescribed herein and it may include a metal catalyst dispersed in amolten salt matrix comprising a eutectic mixture of alkali metal oralkaline earth metal carbonates. In some embodiments, this may include amixture of a transition metal compound and a rare earth metal compoundand a eutectic mixture of alkali metal carbonates or hydroxides. The O₂gas may be introduced to the reactor/reaction as a purified O₂ stream,air, or a mixture of O₂ or air with a diluent gas, wherein the diluentis methane, carbon dioxide, nitrogen, argon, helium, or a combination ofany two or more thereof.

The process provides for the production of olefinic and/or aromaticcompounds from a carbon-containing feedstock. Because thecarbon-containing feedstock may be from a wide variety of materials forprocess, including the processing of recycled plastics, biomass,biowaste, mixed plastics, biomass, and/or biowaste, the olefinic and/oraromatic compounds that are produced may include a wide variety ofunsaturated compounds such as, but not limited to light olefins,α-olefins, terminal dienes, substituted and unsubstituted aromaticcompounds, including single aromatic ring or several aromatic ringcompounds.

Illustrative olefinic and/or aromatic compounds are from a wide range ofmaterials. In some embodiments, the olefinic compounds may be from C₂ toC₂₀ olefins, from C₂ to C₁₆ olefins, or from C₂ to C₁₂ olefins, or fromsubranges of any of these. In some embodiments, the aromatic compoundsmay be from C₆ to C₁₈ aromatics, or from C₆ to C₁₂ aromatics, or fromsubranges of any of these. Illustrative olefinic and/or aromaticcompounds include, but are not limited to, ethene, propene, 1-butene,2-methyl-but-1-ene, 1-n-pentene, 2-methyl-pent-1-ene,3-methyl-pent-1-ene, 1,3-butadiene, 1,3-pentadiene, 1,4-pentadiene,1,3-hexadiene, 1,4-hexadiene, 1,5-hexadiene, benzene, toluene,ethylbenzene, xylenes, styrene, α-methylstyrene, naphthalene, andanthracene.

As noted herein, the carbon-containing feedstock may include, but is notlimited to, any one or more of a refinery range hydrocarbons, a polymer,a biopolymer, biomass, or biowaste. Where the feedstock includes apolymer, illustrative polymers include, but are not limited to thosesuch as polyethylene, polypropylene, polyisobutylene, polybutadiene,polystyrene, poly-α-methylstyrene, polacrylates, poly(meth)acrylates,polyvinyl acetate, and polyvinylchloride. Where the feedstock includes abiopolymer or other bio-based material it may include materials such asfatty acids, triglyceride esters of fatty acids, cellulose, lignin,sugars, animal fat, tissue, and ordure.

Refinery range hydrocarbons are typically defined by their boiling pointrange fractions. For example, light naphtha has an approximate boilingpoint range of 25 to 85° C., heavy naphtha has an approximate boilingpoint range of 85 to 200° C., kerosene has an approximate boiling pointrange of 170 to 265° C., gas oil has an approximate boiling point rangeof 175 to 345° C., and heavy residue has an approximate boiling pointrange of 345 to 656° C. All of these may serve as the feedstock for arefinery range hydrocarbon. In some embodiments where the feedstockincludes a refinery range hydrocarbon, it may include asphalt, vacuumresid, heavy residual oil, paraffin wax, lubricating oil, diesel,kerosene, naphtha, or gasoline. In some embodiments, the feedstock mayinclude n-hexane, n-hexadecane, or white mineral oil.

The process described herein may be generally described by reference toFIGS. 2 and 3 . As shown, the process 200, 300 includes introducing acarbon-containing feedstock 210 to a reactor. Oxygen gas (as O₂, air, orother gas mixtures containing O₂) 220 may be co-fed to the reactor 230that contains a catalyst comprised of a metal compound dispersed in amolten salt matrix of a eutectic mixture of alkali metal or alkalineearth metal carbonates or hydroxides, and the carbon-containingfeedstock undergoes catalytic cracking with oxygen to generate productsof the reaction 240. The products of the reaction include light olefins,other hydrocarbons such as alkanes and oxygenates, hydrogen, carbonmonoxide, carbon dioxide, water, and the like. The products are thenseparated 250 by any of distillation, membrane separation, pressureswing adsorption, or a combination of any two or more thereof, asappropriate. As part of the separation, each of the products may beseparated into a product stream, three of which are shown in FIG. 2 asH₂, CO, CO₂ plus H₂O 260, olefins 270, and alkanes and oxygenatedorganic compounds 280. The olefins, of course, may be collected for usein preparing virgin polymers, or in other applications. The alkanebyproducts, together with the oxygenates, which are composed mostly oflow carbon atom aldehydes such as acetaldehyde and others, as well asketones such as acetone may be used industrially in appropriateapplications; or hydrogenated to alcohols; or recycled back into thecracking process using the optional recycling loop 290 for theadditional conversion to the desired olefins.

As illustrated in FIG. 3 , the process may also include a catalystrecycling loop where spent molten salt catalyst 223 is moved to acatalyst regeneration reactor 221 where oxygen (as O₂, air, or other gasmixtures containing O₂) is reacted with the spent molten salt catalyst.Gases 224 that do not react with the spent molten salt catalyst such asnitrogen gas from air or are a result of the regeneration of thecatalyst, may be vented, and the regenerated molten salt catalyst isthen returned 222 to the reactor 230.

In the process, the temperature inside the reactor system is dependentupon the composition of the catalyst, feed, and desired reactionproducts. Accordingly, the temperature may be from the melting point ofthe eutectic mixture of alkali carbonates and/or hydroxides up to about750° C. This may include a temperature from about 250° C. to about 750°C.

In the process, the pressures inside the reactor system may be low bycomparison to other similar processes. For example, it may be about 20atm or less. In some embodiments, it is from less than 1 atm to about 20atm, from about 1 atm to about 15, or from about 2 atm to about 10 atm.

In the process, the at least one heterogeneous catalyst may be preparedoutside of the reactor system; then loaded into the reactor system tocarry out the catalytic cracking of hydrocarbons.

In another embodiment of the process, the at least one heterogeneouscatalyst is prepared inside the reactor system, by loading the reactorsystem volume with a catalyst precursor mixture and heating itinternally at the process temperature. The catalyst precursor mixturecomprises a salt matrix comprising a eutectic mixture of a mixture ofalkali metal or alkaline earth metal carbonates or hydroxides and ametal catalyst precursor comprising at least one metal compound selectedfrom transition metal compounds, rare-earth metal compounds, or acombination of any two or more thereof.

Also provided is a process for preparing a heterogeneous catalyst. Theprocess includes combining alkali metal or alkaline earth metalcarbonates or hydroxides to form a salt matrix comprising eutectic saltmixture; adding to the salt matrix, at least one metal catalystprecursor to form a catalyst precursor mixture; and heating the catalystprecursor mixture to a temperature of about 250° C. to about 750° C. toform the heterogeneous catalyst comprising a metal catalyst dispersed ina molten salt matrix. In the process, the metal catalyst precursorcomprises at least one metal compound selected from transition metalcompounds, rare-earth metal compounds, or a combination of any two ormore thereof, and the molten salt may also be in a precursor form asnoted above, i.e., the hydroxide form. As noted above, the metalcatalyst may include carbonates or oxide, and it may also include otheroxide structures for the metals such as perovskites and spinels.

The heterogeneous catalyst produced by the process described above isuseful in the process of catalytic cracking of hydrocarbons. Such aprocess of forming the catalyst may be conducted separately (ex-situ)from the process of cracking a hydrocarbon feedstock, or it may be donein the reactor system (in-situ) in which the cracking is conducted.While the in-situ process may be convenient for a batch type reaction,ex-situ processes are more convenient for continuous processes.

The reactor system for the proof of concept was a batch reactor and astirred tank reactor. However, other suitable reactor configurations areconsidered such as falling film column reactors, packed column reactor,plate column reactor, spray tower reactor, and a variety of gas-liquidagitated vessel reactors.

Referring now to FIG. 4 , a general schematic representation of areactor system 400 for processing of polymer waste. The reactor tank405, which is enclosed in the thermal insulation 406, is equipped with amotor and agitation system 410, an O₂ gas enters the reactor through theinlet and supply manifold 420, a catalyst loading port 425 and acatalyst offloading port 430. The catalyst composition is loaded intothe reactor tank 405 via port 425. Polymer waste is chopped and loadedinto a feeder which contains a heated Auger screw extruder 415 throughwhich the polymer is introduced to the reactor tank 405. The reactor ismaintained at a temperature sufficient to maintain the catalyst systemas a molten salt. Solid wastes that are not catalytically converted, andsolid impurities from the polymer may exit the reactor together with theaged catalyst via the port 430 into a holding drum 435. Gaseous productsstream exits the reactor 405 and enters a separator 440. Condensedliquid stream of heavy products 445 (ex. compounds with the dew pointabove 120° C.) is returned from the separator into the reactor, whilethe gaseous stream 450 is directed towards the further separations.

The present invention, thus generally described, will be understood morereadily by reference to the following examples, which are provided byway of illustration and are not intended to be limiting of the presentinvention.

EXAMPLES Example 1. The Catalysts Used in the Study were Prepared by theFollowing Procedure

Catalyst synthesis for the mini-batch reactor screening study: Li₂CO₃(25.68 g), Na₂CO₃ (26.72 g), and K₂CO₃ (27.60 g) were added to atwo-liter mixing vessel for thorough mixing. This mixture iscompositionally similar to a eutectic mixture of the materials in thephase diagram (FIG. 1 ) that melts at about 397° C., and may bedescribed by the chemical formula: Li_(0.86)Na_(0.64)K_(0.50)CO₃. Themelting temperature was confirmed by a differential scanning calorimetry(DSC) analysis. FIG. 6 illustrates the DSC trace for the heating of 25mg sample of the Li, Na, and K carbonates mixture at 20° C. per minuteheating rate. At about 160-165° C., the water of hydration is released,and the three peak grouping (397° C., 408° C., and 420° C.) representsthe three stages of melting of the precursor salts, a process that iskinetically limited when starting with a mixture of individual precursorsalt powders, resulting in the formation of a single-phase eutectic meltat above 420° C. A molten salt catalyst is prepared by combining 80.00 gof this carbonate eutectic mixture with theLi_(0.86)Na_(0.64)K_(0.50)CO₃ eutectic composition; plus 0.40-18.00 g ofeach of the active metal precursor compound that is intended for theformulation inside the mini-batch reactor; before mixing with theeutectic composition, this mixture of catalyst metal precursor compoundsis calcined in air at 600° C. for 2 hrs (for the off-gas evolution,believed to be primarily steam from the crystal hydride dehydration andCO₂ from the transition or rare-earth metal carbonate precursorsconversion to a metal oxide form in the final catalyst state). Forinstance, one molten salt catalyst formulation contained about 80.00 gof the eutectic mixture of alkali carbonate salts and 1.00 g of a barium(II) carbonate powder (BaCO₃), plus about 1.00 g of a copper (II)carbonate powder (CuCO₃·Cu(OH)₂) and 17.00 g of cerium (III) carbonatepowder (Ce₂(CO₃)₃). Another molten salt catalyst formulation containedabout 80.00 g of the eutectic mixture of alkali carbonate salts and 0.40g of BaCO₃, plus about 0.40 g of La₂(CO₃)₃, and 6.80 g of FeCO₃. Yet,another catalyst formulation contained about 80.00 g of the eutecticmixture of alkali carbonate salts and 0.40 g of BaCO₃, plus about 7.20 gof MnCO₃. Table 3 contains the description of catalyst formulationsprepared for the screening study.

Catalyst synthesis for the continuously stirred tank reactor study:First, Li₂CO₃ (642.0 g), Na₂CO₃ (668.0 g), and K₂CO₃ (690.0 g) wereadded to a two-liter volume mixing vessel, where it was mixed thoroughlyto make the alkali-carbonate salts mixture. Then, 25.0 g of Cu₂(OH)₂CO₃,25.0 g of alkali-carbonate eutectic salts mixture, and 425.0 g ofCe₂(CO₃)₃·xH₂O precursor powders were weighted into one liter volumemixing vessel, where it was mixed thoroughly to make the metal catalystprecursors mixture. The content of the vessel was poured into two 500 mlvolume porcelain crucibles. The crucibles were placed into a calcinationoven and calcined at 600° C. for 2 hours (“hr”) using a heating-coolingramp of 5° C./min. The calcination resulted in 18.7 wt % weight loss ofthe original metal catalyst precursors mixture due to decomposition ofthe carbonates to oxides and the loss of crystal hydride water. Lastly,the resulting 386.0 g of the metal catalyst powder was mixed in with1930.0 g of the alkali-carbonate salts eutectic powders mixture insidethe continuously stirred tank reactor vessel immediately before thereaction study.

TABLE 3 Description of catalyst formulations used in the oxycrackingscreening study. Precursor Compound Catalyst Name Weight, g Eu = Li₂CO₃25.68 Li_(0.86)Na_(0.64)K_(0.50)CO₃ Na₂CO₃ 26.72 K₂CO₃ 27.60 Eu′, sameprecursor Li₂CO₃ 642.00 ratios as in Eu Na₂CO₃ 668.00 K₂CO₃ 690.00 Cat.A′ Cu₂(OH)₂CO₃ 25.00 Ce₂(CO₃)₃•xH₂O 425.00 Eu′ 1955.00 Cat. A BaCO₃ 1.00Cu₂(OH)₂CO₃ 1.00 Ce₂(CO₃)₃•xH₂O 17.00 Eu 80.00 Cat. B BaCO₃ 0.40 La(OH)₃0.40 FeCO₃ 6.80 Eu 80.00 Cat. C BaCO₃ 0.40 MnCO₃ 7.20 Eu 80.00 Cat. D(NH₄)₂MoO₄ 0.40 V₂O₅ 7.20 Eu 80.00 Cat. E FeCO₃ 10.00 Cu₂(OH)₂CO₃ 10.00(NH₄)₂MoO₄ 10.00 Eu 70.00 Cat. F NiCO₃ 10.00 MnCO₃ 10.00 CoCO₃ 10.00 Eu70.00

Example 2. Mini-Batch Reactor Screening Study

This example demonstrates that the use of invented catalyst in directoxycracking of various carbon-containing feedstocks increases the extentof cracking and thereby, increases the yield to desired light olefinsand aromatics.

Experimental setup description: Referring now to FIG. 5 . The 23 mmdiameter, 75 mm tall, and 20 ml volume round bottom clear borosilicateglass vials 520 (Ace Glass) make suitable mini-batch reactors forscreening both catalysts and substrates in the oxycracking in moltensalts. After loading with the desired amount of catalyst and reactionsubstrate 522, the vials were sealed with the 20 mm diameter crimp capsequipped with the PTFE-lined silicone septa 521 (Thermo Scientific™SUN-SRi™). The reaction screening assembly consisted of a 6 parallel 25mm diameter 50 mm deep channels aluminum alloy block 505 (Corning LSEDigital Dry Bath Accessory) insulated with the glass wool thermalinsulation layer 510 and affixed on-top of a compact ceramic hot-plate515 (Electron Microscopy Sciences with Corning Pyroceram heatingelement, model Pc220, 25-550° C. range). The set-up was located inside avent hood behind a blast shield for enhanced operator safety. Thetemperature of the aluminum block 505 was controlled by powering the hotplate through an external temperature controller (not shown on the FIG.5 ) (Chemglass Life Sciences J-Kem Temperature Controller, Model 210/T)equipped with a metal-jacketed ⅛″ diameter K-type thermocouple 530 whosetip was inserted into the thermocouple channel in the aluminum block.The 3 grams of a 40 grit SiC powder was added to each of the 6 channelsin the aluminum alloy block in order to provide better thermal contactbetween the vials and the block. A glass vial 525 was filled ˜¼ ofvolume with the Li_(0.86)Na_(0.64)K_(0.50)CO₃ composition eutectic saltsmixture and placed in one of the corner channels in the block. A K-typethermocouple 535 was inserted in the vial; with its tip immersed intothe eutectic material at the bottom. The thermocouple was connected to adigital readout to indicate the temperature of reaction medium in thevials.

Experimental procedure description: A new glass vial is weighted; thenloaded with 10-20 mg of a feedstock and 1100-1250 mg of molten saltcatalyst powder; then, the reactor is sealed using a crimping tool inair for the direct oxycracking, or in the glove box under inert nitrogenatmosphere for the 2-step oxycracking. The vials are arranged in groupsof 2, then loaded using a pair of forceps into the aluminum block thatis maintained at 420° C. for the direct oxycracking, or 500° C. for the2-step oxycracking. The vials are heated inside the alloy block for 15min and then, removed and placed horizontally onto a glass wool blanketto cool. Once at near room temperature, the vials are placed into a vialholder array plate and stored in it until analysis. The analysis isperformed using a GC instrument, and as a part of the analysis each vialis heated to 180° C. for 10 min before the vapor phase is sampled foranalysis. The analysis is also performed using a separate GC-MSinstrument for selected parallel reactor runs.

Product analysis description: Product composition was analyzed using anAgilent 8890 gas chromatograph equipped with a thermal conductivitydetector (TCD) and flame ionization detector (FID). The identity of thecompounds was determined either based on the mass-spectra signaturesmatch with a NIST-MS database on a separate GC-MS instrument for all thecompounds in the refinery gas standard (Restek Refinery Gas Standard #2,Manufacturer #34442) or based on the order of elution following theboiling point of the solutes/compounds (FID) and thermal conductivitydifferences (TCD). The peaks areas obtained by integrating peaks on thegas chromatogram were used in the quantification of hydrocarboncompounds (FID signal) and permanent gases (TCD signal). Morespecifically, the peak areas were converted to molar concentrationsusing the molar response factors (TCD and FID) of various alkane andalkene products estimated from GC calibration with the refinery gasstandard sample, while molar or relative response factors (FID) ofvarious aromatic products were estimated from theoretical effectivecarbon number approach (Journal of Chromatographic Science, Vol. 23,August, 1985). The following equation (10) was used to determine theyield (wt %) of a given compound.Yield(wt %)=Weight(compound)/Weight(feed)×100  (10)

The products obtained during direct oxycracking with Cat. A (from Table3) were analyzed using GC, and the results are reported in Table 4, withproduct stream containing various alkanes, olefins, aromatics andoxygenates viz. hydrogen, methane, ethane, ethylene, propane, propylene,butanes, butenes, pentanes, pentenes, hexanes, carbon oxides and others.The use of catalyst resulted in higher conversions for all thefeedstocks, increasing the overall yield to the desired light olefinsand aromatics, though slightly decreasing the selectivity. Furthermore,the products obtained from parallel reactor runs were also analyzedusing GC-MS to capture a much broader range of products. FIG. 8 and FIG.9 includes the GC-MS traces for the products collected from directoxycracking of olive oil with Cat. E and Cat. F and of n-hexane withCat. A respectively.

TABLE 4 Product mixtures from thermal and catalytic direct oxycrackingof HDPE and n-hexane feedstocks over Cat. A. Product Selectivity,Feedstock: HDPE Feedstock: n-Hexane wt % of total gases None Cat. A NoneCat. A Hydrogen — — — 0.3 Methane 0.5 0.4 9.6 8.8 Ethane — — — —Ethylene 1.5 0.9 7.6 13.3 Propane — — — — Propylene 1.0 1.1 1.3 2.8Butanes 0.3 0.4 — — Butenes 0.6 0.9 0.7 1.2 Pentanes — — — — Pentenes0.3 0.6 0.2 0.4 Hexanes 0.2 0.3 5.8 21.4 Aromaticsª 0.6 2.0 3.0 2.5 CO58.7 1.3 65.5 15.7 CO₂ 36.3 92.2 6.1 33.4 Conversion^(b) 2.6 1.6 42.955.8 5 ^(a)Aromatics is a sum of content of benzene, ethylbenzene,toluene, styrene, xylenes. ^(b)Conversion defined as the total amount offormed gaseous products to the amount of feed.

Example 3. Mini-Batch Reactor Screening Study

This example demonstrates that the use of invented catalyst in 2-stepoxycracking of various carbon-containing feedstocks increases the extentof cracking and thereby, increases the yield to desired light olefinsand aromatics.

Using the same experimental setup described in example 2, the productsobtained during 2-step oxycracking of wide range of feedstocks,including high-density polyethylene (HDPE), low-density polyethylene(LDPE), polypropylene (PP), polyethylene terephthalate glycol (PETG),polystyrene (PS), polyvinyl chloride (PVC), asphalt, vegetable oil (VegOil), n-hexane, n-hexadecane, paper, rubber, polyurethane (PU) andpotato chips, with Cat. A (from Table 3) were analyzed using GC, and theresults are reported in Tables 5A-5G. The use of catalyst resulted inhigher conversions for all the feedstocks, increasing the overall yieldto the desired light olefins and aromatics, though slightly decreasingthe selectivity. Furthermore, the products obtained from parallelreactor runs were also analyzed using GC-MS to capture a much broaderrange of products. FIG. 11 includes the GC-MS traces for the productscollected from 2-step oxycracking of n-hexane, n-hexadecane, PP, PETGand PVC with Cat. A. While the feedstocks like PETG and PVC containheteroatoms like O and Cl, their oxycracking products do not comprise ofO and Cl respectively (from FIG. 11 ). This highlights an additionalsignificant advantage of the invented molten-based catalyst, wherein themolten phase eliminates or significantly decreases the emission of suchheteroatom pollutants into the products or atmosphere by retaining theheteroatoms (like O, Cl, etc.) during the reaction step.

TABLE 5A Product mixtures from thermal and catalytic 2-step oxycrackingof HDPE and LDPE feedstocks over Cat. A. Product Selectivity, Feedstock:HDPE Feedstock: LDPE wt % of total gases None Cat. A None Cat. AHydrogen — 0.9 — 2.4 Methane 5.8 5.1 6.1 6.6 Ethane — — — — Ethylene19.5 13.4 16.9 16.5 Propane — — — — Propylene 26.8 17.1 21.8 20.5Butanes 5.6 2.2 7.3 4.0 Butenes 20.7 12.2 20.7 16.6 Pentanes — — — 0.1Pentenes 11.3 8.1 12.8 9.6 Hexanes 8.1 3.5 7.6 4.5 Aromaticsª 2.1 6.56.9 10.6 CO — 1.2 — 2.3 CO₂ — 29.8 — 6.4 Conversion^(b) 4.6 26.0 6.120.3 ^(a)Aromatics is a sum of content of benzene, ethylbenzene,toluene, styrene, xylenes. ^(b)Conversion defined as the total amount offormed gaseous products to the amount of feed.^(b)Conversion defined as the total amount of formed gaseous products tothe amount of feed.

Thus, 2-step oxycracking of HDPE and LDPE feedstocks over Cat. Aresulted in increased cracking conversion to gaseous products from 4.6%to 26.0% and from 6.1% to 20.3% respectively, thereby increasing theoverall yield to light olefins (more specifically, ethylene andpropylene) and aromatics, albeit at the expense of slightly decreasedselectivity.

TABLE 5B Product mixtures from thermal and catalytic 2-step oxycrackingof PP and PETG feedstocks over Cat. A. Product Selectivity, Feedstock:PP Feedstock: PETG wt % of total gases None Cat. A None Cat. A Hydrogen— 0.3 — 0.5 Methane 4.3 2.0 38.9 1.0 Ethane — — 0.0 — Ethylene 5.9 4.418.0 1.0 Propane — — — — Propylene 38.8 27.3 3.9 0.3 Butanes 0.5 0.6 — —Butenes 22.8 16.8 1.7 0.1 Pentanes — 0.1 — — Pentenes 17.6 31.3 — 0.2Hexanes 4.4 3.2 0.2 — Aromaticsª 5.7 6.6 37.2 11.2 CO — 0.5 — 7.1 CO₂ —6.9 — 78.5 Conversion^(b) 17.4 44.6 3.4 40.9 ^(a)Aromatics is a sum ofcontent of benzene, ethylbenzene, toluene, styrene, xylenes.^(b)Conversion defined as the total amount of formed gaseous products tothe amount of feed.

Thus, 2-step oxycracking of PP and PETG feedstocks over Cat. A resultedin increased cracking conversion to gaseous products from 17.4% to 44.6%and from 3.4% to 40.9% respectively, thereby increasing the overallyield to light olefins (more specifically, ethylene and propylene) andaromatics, albeit at the expense of slightly decreased selectivity.

TABLE 5C Product mixtures from thermal and catalytic 2-step oxycrackingof PS and PVC feedstocks over Cat. A. Product Selectivity, Feedstock: PSFeedstock: PVC wt % of total gases None Cat. A None Cat. A Hydrogen — —0.4 0.7 Methane — 0.1 9.7 3.0 Ethane — — — — Ethylene 1.1 0.2 4.8 1.7Propane — — — — Propylene 0.4 0.1 7.3 1.6 Butanes — — 1.3 0.5 Butenes0.3 0.1 6.9 1.4 Pentanes 4.0 0.7 — — Pentenes — — 1.8 0.6 Hexanes — —1.9 0.5 Aromaticsª 94.3 53.7 65.9 25.7 CO — 0.1 — 1.7 CO₂ — 45.1 — 62.6Conversion^(b) 6.9 38.1 8.7 23.4 ^(a)Aromatics is a sum of content ofbenzene, ethylbenzene, toluene, styrene, xylenes. ^(b)Conversion definedas the total amount of formed gaseous products to the amount of feed.

Thus, 2-step oxycracking of PS and PVC feedstocks over Cat. A resultedin increased cracking conversion to gaseous products from 6.9% to 38.1%and from 8.7% to 23.4% respectively, thereby increasing the overallyield to light olefins (more specifically, ethylene and propylene) andaromatics, albeit at the expense of slightly decreased selectivity.

TABLE 5D Product mixtures from thermal and catalytic 2-step oxycrackingof asphalt and vegetable oil feedstocks over Cat. A. ProductSelectivity, Feedstock: Asphalt Feedstock: Veg Oil wt % of total gasesNone Cat. A None Cat. A Hydrogen — 2.3 0.2 4.4 Methane 21.4 16.7 5.0 6.0Ethane — — — — Ethylene 9.6 12.6 8.2 8.3 Propane — — — — Propylene 15.018.5 10.8 13.0 Butanes 5.0 3.9 2.1 3.6 Butenes 13.6 14.1 8.3 9.9Pentanes 1.1 0.9 — 0.1 Pentenes 6.2 7.4 25.2 33.7 Hexanes 8.7 6.5 4.35.6 Aromatics^(a) 13.8 13.8 6.1 9.7 CO — 3.3 — 5.8 CO₂ 5.4 — 29.8 —Conversion^(b) 5.9 11.8 28.9 32.4 ^(a)Aromatics is a sum of content ofbenzene, ethylbenzene, toluene, styrene, xylenes. ^(b)Conversion definedas the total amount of formed gaseous products to the amount of feed.

Thus, 2-step oxycracking of Asphalt and Veg Oil feedstocks over Cat. Aresulted in increased cracking conversion (and selectivity) to gaseousproducts from 5.9% to 11.8% and from 28.9% to 32.4% respectively,thereby increasing the overall yield to light olefins (morespecifically, ethylene and propylene) and aromatics.

TABLE 5E Product mixtures from thermal and catalytic 2-step oxycrackingof n-hexane and n-hexadecane feedstocks over Cat. A. Feedstock: ProductSelectivity, Feedstock: n-hexane n-hexadecane wt % of total gases NoneCat. A None Cat. A Hydrogen — — — — Methane 0.2 0.4 8.5 3.2 Ethane — — —— Ethylene 0.4 0.6 27.8 10.2 Propane — — — — Propylene 0.5 1.0 22.1 8.0Butanes — — — — Butenes 0.5 0.7 15.5 5.5 Pentanes — — — — Pentenes — —14.8 5.1 Hexanes 98.5 97.4 0.2 0.1 Aromaticsª — — 11.0 4.3 CO — — — —CO₂ — — 0.1 63.6 Conversion^(b) 1.6 2.7 6.4 16.8 ^(a)Aromatics is a sumof content of benzene, ethylbenzene, toluene, styrene, xylenes.^(b)Conversion defined as the total amount of formed gaseous products tothe amount of feed.

Thus, 2-step oxycracking of n-hexane and n-hexadecane feedstocks overCat. A resulted in increased cracking conversion to gaseous productsfrom 1.6% to 2.7% and from 6.4% to 16.8% respectively, therebyincreasing the overall yield to light olefins (more specifically,ethylene and propylene) and aromatics, albeit at the expense of slightlydecreased selectivity for the case of n-hexadecane feedstock.

TABLE 5F Product mixtures from thermal and catalytic 2-step oxycrackingof paper and rubber feedstocks over Cat. A. Product Selectivity,Feedstock: Paper Feedstock: Rubber wt % of total gases None Cat. A NoneCat. A Hydrogen — 0.6 — 1.3 Methane 31.5 1.5 10.8 10.0 Ethane 0.0 — — —Ethylene 7.8 0.4 5.3 6.2 Propane — — — — Propylene 12.5 0.4 7.6 9.2Butanes 1.8 0.1 1.4 1.5 Butenes 12.6 0.2 7.4 7.3 Pentanes 0.2 — 0.2 0.2Pentenes 3.7 — 5.9 4.7 Hexanes 8.0 0.1 19.2 16.8 Aromaticsª 22.0 0.642.2 40.0 CO — 1.2 — 2.7 CO₂ — 95.0 — — Conversion^(b) 3.1 31.7 16.116.5 ^(a)Aromatics is a sum of content of benzene, ethylbenzene,toluene, styrene, xylenes. ^(b)Conversion defined as the total amount offormed gaseous products to the amount of feed.

Thus, 2-step oxycracking of paper and rubber feedstocks over Cat. Aresulted in increased cracking conversion to gaseous products from 3.1%to 31.7% and from 16.1% to 16.5% respectively, thereby increasing theoverall yield to light olefins (more specifically, ethylene andpropylene) and aromatics, albeit at the expense of slightly decreasedselectivity for the case of paper feedstock.

TABLE 5G Product mixtures from thermal and catalytic 2-step oxycrackingof PU and potato chips feedstocks over Cat. A. Product Selectivity,Feedstock: PU Feedstock: Chips wt % of total gases None Cat. A None Cat.A Hydrogen — 7.2 — 2.1 Methane 7.8 2.2 23.8 5.4 Ethane — — — — Ethylene6.6 2.6 12.1 4.3 Propane — — — — Propylene 47.6 5.9 15.0 5.4 Butanes 1.60.1 3.8 1.8 Butenes 25.4 4.3 13.4 4.3 Pentanes — — 0.2 0.1 Pentenes 0.90.4 6.3 2.8 Hexanes 3.0 0.9 8.7 2.2 Aromaticsª 7.0 3.6 16.7 7.4 CO —15.8 — 6.6 CO₂ — 56.9 — 57.7 Conversion^(b) 6.5 15.5 6.0 19.5^(a)Aromatics is a sum of content of benzene, ethylbenzene, toluene,styrene, xylenes. ^(b)Conversion defined as the total amount of formedgaseous products to the amount of feed.

Thus, 2-step oxycracking of PU and potato chips feedstocks over Cat. Aresulted in increased cracking conversion to gaseous products from 6.5%to 15.5% and from 6.0% to 19.5% respectively, thereby increasing theoverall yield to light olefins (more specifically, ethylene andpropylene) and aromatics, albeit at the expense of slightly decreasedselectivity.

Example 4. Mini-Batch Reactor Screening Study

This example demonstrates the use of various types of invented catalystsin 2-step oxycracking to tune the product stream/distribution towardslight olefins and aromatics.

Using the same experimental setup described in example 2, the productsobtained during 2-step oxycracking of HDPE feedstock with Cat. A, Cat. Band Cat. C (from Table 3) were analyzed using GC, and the results arereported in Table 6. The product distribution (more specifically, lightolefins and aromatics) is found to be a strong function of the type ofcatalyst. Furthermore, the products obtained from parallel reactor runswere also analyzed using GC-MS to capture a much broader range ofproducts. FIG. 10 includes the GC-MS traces for the products collectedfrom 2-step oxycracking of HDPE with Cat. A, Cat. B, Cat. C and Cat. D.

TABLE 6 Product mixtures from thermal and catalytic 2-step oxycrackingof HDPE feedstock over various catalysts (Cat. A, Cat. B, Cat. C).Product Selectivity, Feedstock: HDPE wt % of total gases None Cat. ACat. B Cat. C Hydrogen — 0.9 — — Methane 5.8 5.1 4.7 1.2 Ethane — — — —Ethylene 19.5 13.4 12.3 3.2 Propane — — — — Propylene 26.8 17.1 15.9 4.0Butanes 5.6 2.2 2.0 0.6 Butenes 20.7 12.2 11.3 3.0 Pentanes — — — —Pentenes 11.3 8.1 7.2 1.9 Hexanes 8.1 3.5 3.5 0.9 Aromaticsª 2.1 6.5 6.51.4 CO — 1.2 0.8 0.1 CO₂ — 29.8 35.8 83.8 Conversion^(b) 4.6 26.0 29.185.8 ^(a)Aromatics is a sum of content of benzene, ethylbenzene,toluene, styrene, xylenes. ^(b)Conversion defined as the total amount offormed gaseous products to the amount of feed.

While the cracking conversion to gaseous products from 2-stepoxycracking of HDPE feedstock increased from Cat. A to Cat. B to Cat. C,the selectivity to desired light olefins (more specifically, ethyleneand propylene) decreased from Cat A. to Cat. B to Cat. C, and thus,resulting in different overall yields to light olefins and aromatic forCat. A, Cat. B and Cat. C.

Example 5. Bench-Scale Stirred Tank Reactor Study

Liquid n-hexadecane feedstock was introduced via a syringe pump(Teledyne ISCO 1000D) at a rate of 0.77 gram per minute together with400 standard centimeter cube per minute (sccm) flow of N₂ diluentthrough a 0.95 centimeter diameter stainless steel dip tube. The diptube terminated near the bottom of a 10.0 centimeter diameter and 62.2centimeter height stainless steel stirred tank reactor. The reactorcontained 2316 gram a molten catalyst, Cat. A′, under a constantstirring by a 5 centimeter diameter three-blade hydrofoil impellerlocated at the bottom of the molten catalyst bath and operated at 200rotations per minute. The height of the molten catalyst bath was about14 centimeters, while the overall height of reactor heated to thereaction temperature was about 28 centimeters. The molten salt catalystwas prepared inside the reactor prior to the experiment by first loadingthe reactor with 1930 gram of the alkali-carbonate salts eutecticprecursors mixture powder, then melting the powder into a molteneutectic by heating it to 450° C., then by adding 386 gram of the metalcatalyst precursor powder into the molten salt eutectic under stirringand N₂ diluent purging. The catalyst was conditioned prior tooxycracking reactor experiment by heating the reactor to 750° C. under2000 sccm flow of air, and maintaining it at the temperature for 2hours. Then, the gas feed was switched to 400 sccm flow of N₂ diluent,and the reactor was allowed to cool to a desired reaction temperature.The molten salt catalyst temperature was monitored by a K-typethermocouple inserted through an access port at the bottom of thereactor, located just beneath the stirring impeller. The effluent gasflow first passed through a stainless steel condenser that wasmaintained at 5-15° C., then through a zone of sampling ports of theon-line process GC (Agilent 8890), and in-line process mass-spectrometer(MS, Pfeiffer Vacuum ThermoStar), before passing through a mineral oilbubbler, then vented into the atmosphere. The process GC was anidentical instrument to the one used in the mini-batch reactor screeningstudy. It was calibrated using a similar gas standard (Restek RefineryGas Standard #2), which was also used for calibrating the process MSinstrument. The content of the residual coke in the catalyst wasobtained by integrating the 14 amu/z and 44 amu/z signals correspondingto N₂ and CO₂ ionized species concentration in the signal obtained fromthe process MS output. The quantity of liquid products accumulating inthe condenser was measured gravimetrically. The duration of theoxycracking reaction step was 20 min, after which the feed of the liquidwas discontinued and the reactor was purged with N₂ dilutant at 400 sccmfor 15 minutes. Then, the N₂ flow rate was then increased to 2000 sccmfor an additional 10 minutes to remove any residual volatile materialsfrom the internal volume of the reactor. After the purge was completed,the catalyst regeneration step was performed by feeding air into thereactor through the dip tube at 900 sccm for 20-30 min duration,re-oxidizing the molten catalyst and combusting the residual coke. Thefurnace temperature was maintained the same between the oxycracking andcatalyst regeneration reaction steps.

TABLE 7 Product composition from catalytic 2-step oxycracking of n-hexadecane in the presence of molten salt catalyst, Cat. A′, in astirred tank reactor at four different reaction temperatures. ProductYield, wt % Temperature, C. on Feed 500 600 650 700 Hydrogen — 0.1 0.20.4 Methane 0.3 6.2 11.8 17.9 Ethane 0.7 7.2 10.9 11.9 Ethylene 0.8 17.725.9 28.9 Propane 0.4 1.1 1.7 1.4 Propylene 0.9 15.4 22.8 19.7 Butanes0.1 0.2 0.3 0.2 Butenes 0.6 9.5 10.8 7.0 Pentanes — 0.1 0.2 0.1 Pentenes0.7 5.8 4.4 1.6 Hexanes — 0.0 1.8 1.9 Hexenes 0.9 4.9 3.1 0.7 Aromaticsª— 1.1 5.1 9.8 CO — — — 0.2 CO₂ — 0.6 0.9 1.6 Coke — 0.8 1.8 2.4 Liquids94.6 34.7 4.0 0.6 ^(a)Aromatics is a sum of content of benzene,ethylbenzene, toluene, styrene, xylenes.

A summary of results of the 2-step oxycracking of n-hexadecane using amolten salt catalyst which contains a copper-cerium metal catalystcomposition, is presented in Table 7. The results indicate a high yieldof light olefins and high conversion of the feedstock that can beobtained when using the molten salt composition and process whenperforming the process at temperatures at above 600° C. and at below700° C.

Example 6. Bench-Scale Stirred Tank Reactor Study

Solid polymer feedstocks were introduced via a generic 3D printer headfeeder as a 1.75 millimeter diameter filament at a rate in the rangebetween 0.75 and 1.4 gram per minute together with 400 sccm flow of N₂diluent which were either co-fed through the dip tube, or were fedseparately: the diluent through the dip tube and the polymer filamentwas fed from the headspace above the molten catalyst bath. The plasticfeedstocks used in the experiment included: including high-densitypolyethylene (HDPE), polypropylene (PP), polyethylene terephthalateglycol (PETG), and acrylonitrile butadiene styrene (ABS).

TABLE 8 Product composition from catalytic 2-step oxycracking of variouscarbon-containing feedstocks: HDPE. PP, PETG, and ABS over the Cat. A′formulation at 650° C. Product Yield, Feedstock wt% on Feed HDPE PP PETGABS Hydrogen 0.2 0.3 0.2 0.6 Methane 6.8 13.1 2.0 5.1 Ethane 4.5 7.7 0.32.3 Ethylene 13.7 12.1 1.4 5.7 Propane 1.0 2.7 — 0.5 Propylene 12.9 21.60.4 4.4 Butanes 0.2 0.7 0.8 0.1 Butenes 5.9 14.6 0.3 3.2 Pentanes 0.21.0 0.1 0.1 Pentenes 1.2 4.3 0.2 0.5 Hexanes 0.1 0.1 0.0 — Hexenes 0.80.3 0.0 0.3 Aromatics^(a) 9.0 6.4 21.4 6.8 CO 0.0 0.0 18.6 1.6 CO₂ 1.24.7 89.1 7.4 Coke 2.4 2.8 3.1 4.4 Liquids 40.7 16.0 42.5 68.3 Feed rate,g/min 1.38 0.83 0.93 0.79 ^(a)Aromatics is a sum of content of benzene,ethylbenzene, toluene, styrene, xylenes.

The products obtained during 2-step oxycracking were analyzed using GC,and the results are reported in Table 8. The liquid products compositionfor selected experiments was analyzed using the headspace GC-MS analysis(FIG. 12 ). The use of the oxycracking process with the molten saltcatalyst affords high extents of conversion to vapor-phase products,which are dominated by light olefins and aromatic compounds. Forinstance, the 2-step oxycracking of polyolefinic feedstocks: HDPE andPP, produced high yields of light olefins. The processing ofstyrene-containing co-polymer produced primarily light aromatics,including the styrene monomer, while the processing of PETG alsoproduced mostly aromatics, plus only a minor amounts of actophenone, andno appreciable amounts of other oxygenated organic products.

While certain embodiments have been illustrated and described, it shouldbe understood that changes and modifications may be made therein inaccordance with ordinary skill in the art without departing from thetechnology in its broader aspects as defined in the following claims.

The embodiments, illustratively described herein may suitably bepracticed in the absence of any element or elements, limitation orlimitations, not specifically disclosed herein. Thus, for example, theterms “comprising,” “including,” “containing,” etc. shall be readexpansively and without limitation. Additionally, the terms andexpressions employed herein have been used as terms of description andnot of limitation, and there is no intention in the use of such termsand expressions of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the claimed technology.Additionally, the phrase “consisting essentially of” will be understoodto include those elements specifically recited and those additionalelements that do not materially affect the basic and novelcharacteristics of the claimed technology. The phrase “consisting of”excludes any element not specified.

The present disclosure is not to be limited in terms of the particularembodiments described in this application. Many modifications andvariations may be made without departing from its spirit and scope, aswill be apparent to those skilled in the art. Functionally equivalentmethods and compositions within the scope of the disclosure, in additionto those enumerated herein, will be apparent to those skilled in the artfrom the foregoing descriptions. Such modifications and variations areintended to fall within the scope of the appended claims. The presentdisclosure is to be limited only by the terms of the appended claims,along with the full scope of equivalents to which such claims areentitled. It is to be understood that this disclosure is not limited toparticular methods, reagents, compounds, compositions, or biologicalsystems, which can of course vary. It is also to be understood that theterminology used herein is for the purpose of describing particularembodiments only, and is not intended to be limiting.

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognize thatthe disclosure is also thereby described in terms of any individualmember or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range may be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein maybe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the like,include the number recited and refer to ranges which may be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember.

All publications, patent applications, issued patents, and otherdocuments referred to in this specification are herein incorporated byreference as if each individual publication, patent application, issuedpatent, or other document was specifically and individually indicated tobe incorporated by reference in its entirety. Definitions that arecontained in text incorporated by reference are excluded to the extentthat they contradict definitions in this disclosure.

Other embodiments are set forth in the following claims.

What is claimed is:
 1. A process for the catalytic cracking of acarbon-containing feedstock, the process comprising: contacting, in areactor system, the carbon-containing feedstock with a heterogeneouscatalyst composition, said contacting occurring in the presence of anoxidant, to generate a product chemical compound; and collecting theproduct chemical compound, wherein: the heterogeneous catalystcomposition comprises a metal catalyst dispersed in a molten salt matrixcomprising a eutectic mixture of alkali metal or alkaline earth metalcarbonates or hydroxides; and the metal catalyst comprises a transitionmetal compound and a rare-earth metal compound.
 2. The process of claim1, which is an autothermal process.
 3. The process of claim 1, whereinthe contacting is conducted at a temperature of about 750° C. or less.4. The process of claim 1, which is a continuous process, asemi-continuous process, or a batch process.
 5. The process of claim 1,wherein the product chemical compound comprises light olefins,α-olefins, terminal dienes, substituted and unsubstituted aromaticcompounds, aldehydes, oxygenates, or a combination thereof.
 6. Theprocess of claim 1, wherein the product chemical compound comprisesethene, propene, 1-butene, 2-methyl-but-1-ene, 1-n-pentene, 1-n-hexene,2-methyl-pent-1-ene, 3-methyl-pent-1-ene, 1,3-butadiene, 1,3-pentadiene,1,4-pentadiene, 1,3-hexadiene, 1,4-hexadiene, 1,5-hexadiene, benzene,toluene, ethylbenzene, xylenes, styrene, α-methylstyrene, naphthalene,anthracene, or a combination thereof.
 7. The process of claim 1, whereinthe carbon-containing feedstock comprises a polymer comprisingpolyethylene, polypropylene, polyisobutylene, polybutadiene,polystyrene, poly-α-methylstyrene, polacrylates, poly(meth)acrylates,polyvinylchloride, polyethylene terephthalate, or a mixture of any twoor more thereof.
 8. The process of claim 1, wherein thecarbon-containing feedstock comprises a refinery range hydrocarboncomprising asphalt, vacuum resid, heavy residual oil, paraffin wax,pyrolysis wax, lubricating oil, diesel, kerosene, naphtha, gasoline, ora combination thereof.
 9. The process of claim 1, wherein thecarbon-containing feedstock comprises a refinery range hydrocarboncomprising n-hexane.
 10. The process of claim 1, wherein thecarbon-containing feedstock comprises a refinery range hydrocarboncomprising n-hexadecane.
 11. The process of claim 1, wherein thecarbon-containing feedstock comprises lignin, fatty acid, plant-basedoil, municipal solid waste, paper waste, or a mixture of any two or morethereof.
 12. The process of claim 1, wherein the oxidant comprises atleast one member selected from the group consisting of O₂, NO_(x),SO_(x), a nitrate salt, hydrogen peroxide, an organic peroxide, and anon-metal element oxide, such as boron oxide, nitrogen oxide, phosphorusoxide, sulfur oxide, chlorine oxide, and bromine oxide.
 13. The processof claim 1, wherein the oxidant is oxygen and is introduced to thereactor as a purified O₂ stream, air, or a mixture of O₂ or air with adiluent, wherein the diluent is methane, carbon dioxide, nitrogen,argon, helium, or a mixture thereof.
 14. The process of claim 1, whereinthe reactor system comprises a single reactor or at least a firstreactor and a second reactor in series.
 15. The process of claim 1,wherein the reactor system comprises a single reactor, and theheterogeneous catalyst is contacted with the carbon-containingfeedstock.
 16. The process of claim 1, wherein the reactor systemcomprises a first reactor and a second reactor in series, and aheterogeneous catalyst composition in the first reactor is the same asor different than a heterogeneous catalyst composition in the secondreactor.
 17. The process of claim 1, wherein the heterogeneous catalystcomposition is prepared outside of the reactor system; then loaded intothe reactor system to carry out the catalytic cracking of hydrocarbons.18. The process of claim 1, wherein the heterogeneous catalyst isprepared inside the reactor system, by loading the reactor system volumewith a catalyst precursor mixture and heating it internally at theprocess temperature, and wherein the catalyst precursor mixturecomprises a salt matrix comprising a eutectic mixture of alkali metal oralkaline earth metal carbonates or hydroxides and a metal catalystprecursor comprising a transition metal compound and a rare-earth metalcompound.
 19. The process of claim 18, wherein the metal catalystprecursor comprises a carbonate of Ce.
 20. The process of claim 18,wherein the metal catalyst precursor comprises Cu and Ce carbonates, andthe salt matrix comprises a mixture of Li, Na, and K carbonates orhydroxides.
 21. The process of claim 18, wherein the metal catalystprecursor comprises a mixture of Cu₂(OH)₂CO₃ and Ce₂(CO₃)₃·xH₂O, and thesalt matrix comprises of a mixture of Li₂CO₃, Na₂CO₃, and K₂CO₃.
 22. Theprocess of claim 18, wherein the metal catalyst precursor comprises amixture of CuCO₃ and Ce(CO₃)₂, and the salt matrix comprises of amixture of Li₂CO₃, Na₂CO₃, and K₂CO₃.
 23. The process of claim 1,wherein the metal catalyst comprises Cu and Ce in a mol % ratio of about0.10-0.20:1.00, respectively.